Magnetic data storage devices, such as hard disk drive (HDD) storage devices include a front-end system 10 (see FIG. 1(a)) which includes one or more read/write transducer(s) for reading and writing magnetic-data transitions in the magnetic media. The read transducer 23 and write transducer 24 are also called read head and write head or read element and write element. The part that includes the read/write transducer is typically called a slider 14. The sliders 14 are mounted on a mechanical suspension (not shown) which are then attached to a mechanical arm (actuator) (not shown) that positions the transducers over tracks on the rotating disks (not shown) which support the magnetic media film (not shown).
The electrical signals to and from the read and write transducers are processed by corresponding electronic circuitry in the read amplifier 12 and write driver transmitter 22. The write transducer 24 is an inductive coil that writes the electrical data-current signal in the media by creating a corresponding magnetic field and is considered the receiver for the write signal. The electrical data-current signal for the write transducer is created by the write driver transmitter 22 which in this example includes a differential-signal write driver 13 with source termination resistors 29a and 29b, as shown in FIG. 1(b). The read/write channel 11 reads data from the read amplifiers 12 and supplies data signals to the write driver transmitter 22. These electrical signals travel along electrically conductive paths, attached to a movable actuator (not shown), and then through the front-end interconnect 15.
FIG. 1(b) is a simplified illustration of the selected components making up the transmission-line path in the front-end interconnect 15 in a prior-art disk drive. The front-end interconnect 15 typically includes a chip-carrier interconnect 41, a suspension interconnect 42 and a gimbal interconnect 43 before reaching the read/write transducer lead pads (not shown) on the outside of the slider 14. The chip-carrier interconnect 41 impedance component is shown as ZA 32. The suspension interconnect 42 impedance is shown as impedance components 35 and 38 with a value of ZB and ZC respectively. As seen in FIG. 1(b), the gimbal interconnect 43 is a subset of the suspension interconnect 42 and is shown as impedance component 38 with a value of ZC.
Electrically conductive traces are included as part of the front-end interconnect 15, and they connect the read/write transducer lead pads to the read/write electronics. The suspension interconnect 42 is typically a three layer laminate structure (not shown). The laminate layers may include a metallic signal conductor layer from which the afore-mentioned conductive traces are formed, an insulating dielectric layer, and a conductive metallic substrate layer that supports the dielectric layer.
The various electrically conductive trace structures form a transmission-line path between the write driver transmitter 22 and the write transducer 24 in the slider 14. An ideal front-end interconnect 15 should not require compensation, but in practical devices cost and technology constraints lead to discontinuities or impedance variations being present along the signal path. Prior art teaching for impedance matching in this transmission-line path (between the write driver transmitter 22 and the write transducer 24) have forced a uniform characteristic impedance (ZA=ZB=ZC) along the signal path to reduce signal distortion and minimize signal reflections at the write driver transmitter 22, as shown in FIG. 3 (a), which will be discussed further below.
Prior art has also taught that using a single-cable interconnect impedance level has the advantages of decreased signal reflection and loss by avoiding discontinuities at junctures (since it has no junctures) and by having one constant impedance level along the entire single-cable.
Impedance matching can use discrete elements but transmission lines and stub traces (stubs) are sometimes preferable for high-frequency applications and/or small geometries. Stubs are dead-end pieces of transmission line added solely for a reactive lump effect. The two stub types are open-end (ZL=infinite) and short-end (ZL=0). In general, an open-end stub is capacitive and a short-end stub is inductive. FIGS. 4 and 5 illustrate different configurations of stubs, which will be discussed below.
U.S. Pat. No. 5,608,591 by Klaassen describes an integrated transducer-electronics suspension interconnect for a data recording disk drive. This type of suspension interconnect is a multi-layer laminate structure including electrically conductive traces that connect to the write transducer. Sudden changes in the characteristic impedance of these traces are avoided to minimize signal reflections. To achieve this, the width of the traces is shaped accordingly to prevent abrupt changes in the trace bonding areas, apertures and other mechanical obstructions in the suspension interconnect. Also, changes in the traces' direction are gradual to avoid signal reflection. Klaassen '591 teaches a configuration for compensating for sudden impedance changes in the suspension interconnect only. Although today, there are other suspension interconnect designs that avoid such abrupt changes in impedances levels.
U.S. Pat. No. 6,791,429 by Mikalauskas describes counteracting a transmission-line parasitic-element discontinuity by introducing a suitable amount of delay in the transmission line by way of correction impedance. The delay is calculated by taking into account, at least in part, the correction impedance and the parasitic-element effect. The correction transmission line includes an inductance or a capacitance, based on the characteristics of the parasitic element, added to a portion of the transmission line at which the parasitic element is present. The correction transmission line is positioned in the signal transmission line before or after the parasitic element, which can be a juncture, via or hinge.
Recent developments in low-impedance suspension interconnects and low-power write front-end systems create the need for improved impedance control for the complete front-end signal path or front-end interconnect.